Index: llvm/trunk/include/llvm/CodeGen/MachineDominators.h
===================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineDominators.h
+++ llvm/trunk/include/llvm/CodeGen/MachineDominators.h
@@ -216,6 +216,8 @@
 
   void releaseMemory() override;
 
+  void verifyAnalysis() const override;
+
   void print(raw_ostream &OS, const Module*) const override;
 
   /// \brief Record that the critical edge (FromBB, ToBB) has been
@@ -239,6 +241,27 @@
            "A basic block inserted via edge splitting cannot appear twice");
     CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
   }
+
+  /// \brief Returns *false* if the other dominator tree matches this dominator
+  /// tree.
+  inline bool compare(const MachineDominatorTree &Other) const {
+    const MachineDomTreeNode *R = getRootNode();
+    const MachineDomTreeNode *OtherR = Other.getRootNode();
+
+    if (!R || !OtherR || R->getBlock() != OtherR->getBlock())
+      return true;
+
+    if (DT->compare(*Other.DT))
+      return true;
+
+    return false;
+  }
+
+  /// \brief Verify the correctness of the domtree by re-computing it.
+  ///
+  /// This should only be used for debugging as it aborts the program if the
+  /// verification fails.
+  void verifyDomTree() const;
 };
 
 //===-------------------------------------
Index: llvm/trunk/lib/CodeGen/MachineDominators.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MachineDominators.cpp
+++ llvm/trunk/lib/CodeGen/MachineDominators.cpp
@@ -15,9 +15,20 @@
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/ADT/SmallBitVector.h"
+#include "llvm/Support/CommandLine.h"
 
 using namespace llvm;
 
+// FIXME: Always verify dominfo if expensive checking is enabled.
+#ifdef EXPENSIVE_CHECKS
+static bool VerifyMachineDomInfo = false;
+#else
+static bool VerifyMachineDomInfo = false;
+#endif
+static cl::opt<bool, true> VerifyMachineDomInfoX(
+    "verify-machine-dom-info", cl::location(VerifyMachineDomInfo),
+    cl::desc("Verify machine dominator info (time consuming)"));
+
 namespace llvm {
 template class DomTreeNodeBase<MachineBasicBlock>;
 template class DominatorTreeBase<MachineBasicBlock>;
@@ -57,6 +68,11 @@
   DT->releaseMemory();
 }
 
+void MachineDominatorTree::verifyAnalysis() const {
+  if (VerifyMachineDomInfo)
+    verifyDomTree();
+}
+
 void MachineDominatorTree::print(raw_ostream &OS, const Module*) const {
   DT->print(OS);
 }
@@ -125,3 +141,17 @@
   NewBBs.clear();
   CriticalEdgesToSplit.clear();
 }
+
+void MachineDominatorTree::verifyDomTree() const {
+  MachineFunction &F = *getRoot()->getParent();
+
+  MachineDominatorTree OtherDT;
+  OtherDT.DT->recalculate(F);
+  if (compare(OtherDT)) {
+    errs() << "MachineDominatorTree is not up to date!\nComputed:\n";
+    print(errs(), nullptr);
+    errs() << "\nActual:\n";
+    OtherDT.print(errs(), nullptr);
+    abort();
+  }
+}
Index: llvm/trunk/test/CodeGen/AArch64/tailmerging_in_mbp.ll
===================================================================
--- llvm/trunk/test/CodeGen/AArch64/tailmerging_in_mbp.ll
+++ llvm/trunk/test/CodeGen/AArch64/tailmerging_in_mbp.ll
@@ -1,4 +1,4 @@
-; RUN: llc <%s -march=aarch64 | FileCheck %s
+; RUN: llc <%s -march=aarch64 -verify-machine-dom-info | FileCheck %s
 
 ; CHECK-LABEL: test:
 ; CHECK:       LBB0_7: